<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <button onclick="handle()">请求</button>

  <script>
    function handle() {
      let xhr = new XMLHttpRequest();
      xhr.open('GET', 'http://localhost:3000', true);
      xhr.send()
      xhr.onreadystatechange = function () {
        if (xhr.readyState === 4 && xhr.status === 200) {
          console.log(console.log(xhr.responseText));
        }
      }
    }
  </script>
</body>

</html>